Articles of furniture such as stools or chairs which allow a user to rock forward, backward and sideways are generally known. A tiltable stool is typically configured to be used on a generally horizontal surface such as a floor. The stool comprises a top section providing seat and a base section comprising a rounded bottom surface configured to support the stool on the floor.
The base section may be a weighted base which has a downwardly convex lateral surface area to support the stool upon contacting the floor when the stool is tilted out of its normal upright position. In that normal position the stool rests on the floor with a flat or concave area of its base. The weighting of the base is so chosen that the center of gravity of the stool comes to lie inwardly of the perimeter of the central contact area in its tilted state. The support areas may be contiguous, thus forming part of a continuous annular surface, or may be peripherally spaced apart, as by being individually disposed on three or more legs projecting generally radially from the base. Such stools are generally described in U.S. Pat. No. 3,312,437 and in US patent application publication US 2013/0320727.
The conventional stools typically assume an upright normal position when unoccupied. The upright position is obtained by a resetting force which acts on the stool when tilted out of its normal upright position. The resetting force is caused by coordinating the center of gravity of the stool with the fixed shape of its base such that the center of gravity assumes its lowest position when the stool is upright. Typically, the resetting force is selected based on a desired characteristic of an unoccupied stool.
The rounded base of conventional stools have several disadvantages: They may cause noise when the stool is tilted, they require a relatively large and heavy base. The base may slide or roll away due to a small contact surface with the floor, and the stool generally provides insufficient support for a user when tilting out of the upright position, making it undesirable or even dangerous in particular for elderly users.
Attempts have been made to address the inherent disadvantages of a fixedly formed rounded base by using an inflatable base. An exemplary seating arrangement having an inflatable rubber ring is disclosed in U.S. Pat. No. 6,644,742. The inflatable base requires occasional reinflation, which is not practical. It may also be prone to outgassing and cause an undesirable odor.
Also, bases made of foam have been proposed, but those do not address the lack of support for a user to maintain a generally upright seating position and do not adjust to a user's weight.